Embodiments of the invention relate generally to the field of downdraft biomass gasification. More specifically, embodiments of the invention relate to biomass gasification in modular, portable, distributed biomass gasifiers that produce a low tar fuel gas with low emissions, and no toxic waste streams.
Gasification typically involves the oxidization or conversion of carbon-based biomass feedstock to gas or other usable fuel. The resulting gas can be used to generate electricity, or as a raw material to produce chemicals and liquid fuels. Typically, feedstock such as wood chips or other biomass is screened to remove undesirable material. The feed is dried, and processed in a gasifier to produce fuel.
Commonly used techniques for biomass gasification often are hampered by the inability to control the variables of gasification, and thus result in the generation of a fuel gas contaminated with high levels of tars. In many current gasifier systems such high levels of tars require the use of gas clean-up systems that most often incorporate water-based scrubbers and/or large sawdust or sand-bed filters. These components can add cost, complexity, and increase the size of the system footprint. Furthermore, the tar-laden water effluent, or large volumes of sand or sawdust contaminated with tars, often need to be cleaned up or treated as a hazardous waste stream in many countries in general, and the USA in particular.
What is more, current approaches for gasification often do not provide effective gas cooling, which can lead to unclean fuel gas. The cooling of the hot producer gas is a difficult heat transfer problem from a practical point of view. Unequal temperatures and the resulting thermal expansion and contraction of different parts of a tube-and-shell heat exchanger often require provisions for stress relief, when operating with large temperature differences between the two fluid flows. Current techniques also often involve water scrubbing to remove residual tars and chars from producer gases. Unfortunately, these materials are very fine aerosols and particles, which are difficult to remove by this method.
Another shortcoming of distributed fuel gas generation systems is the inability to control them via a communications network to monitor operations and optimize performance while increasing the ability to diagnose and implement rapid repairs. This inability to monitor and control fuel gas generation via a communications network, either local or wide area, can increase the labor costs of operation while reducing revenues due to increased times to recover from system outages.
What is needed are systems and methods for gasification that can accurately control variables of gasification, provide effective gas cooling, operate without the use of scrubbing liquid, and accommodate computer control of a networked group of modular biopower systems. Embodiments of the present invention provide solutions to at least some of these needs.